You can add this code to your cover.xml or cover.html:
Code:
<style type="text/css">
/*<![CDATA[*/
@page {padding: 0pt; margin: 0pt;}
body.nb {padding: 0pt; margin: 0pt;}
/*]]>*/
</style>
It has to go in the xml or html head before the line with the closing tag </head>. Then you have to change the line with <body> to <body class="nb">
If there is a line starting with <link href="../Styles/ in the head (before </head>) then delete the complete line.
That's it.
An easier way is to copy the cover.xml from the file I attached earlier in the thread and put it in the other books. Make shure that the cover image is named cover.png and resolution is 800x600.